1. Field of the Invention
The present invention relates to a motor controlling apparatus, and in particular to a motor controlling apparatus for suppressing vibrations by compensating a commanded position by multiplying a commanded acceleration with a gain determined from constants of the mechanical system.
2. Description of the Related Art
Conventionally, in motor control apparatuses for driving a machine with a motor, a servo control system includes a low-pass filter or notch filters to deal with high-frequency mechanical resonance. These filters are deployed in the control loop of the servo control system, and provided not for compensating position commands but aiming at improvement of the response and stability of the servo control system.
On the other hand, in order to deal with low-frequency resonance, techniques for using smooth commands, techniques of processing commands with notch filters, techniques using an input shaping method for commands and others have been used. These are, differing from countermeasure against high-frequency resonance, designed to cut off or sufficiently reduce the energy of resonance frequencies of the mechanical system, from the position command given to the servo control system.
Further, there is a method of controlling an inertial system by setting up an operation amount for vibration suppressing control by multiplying acceleration command information by a predetermined gain and adding the operation amount for vibration suppressing control to the position command (e.g., Japanese Laid-open Patent Publication No. 2010-88290 A).
In the motor control apparatus in machine tools, generally, PTP (Point to Point) control without regards to a moving path, or path control that controls the machine position along a given moving path, is carried out. When a motor control apparatus performs path control, it is unpreferable that the servo control system greatly deviates from the commanded path programmed by the user.
A case in which time-sequential position commands are given to a certain servo control axis will be taken into consideration. The purpose of the servo control system is to drive a machine in accordance with the time-sequential position commands. However, mechanical resonance sometimes prevents the servo control system from driving a machine exactly on the commanded position. The vibration remains as residual vibration after the axis is stopped, causing problems such as forming a stripe pattern on the workpiece being machined if the machine tool is in machining operation.
When conventional techniques such as notch filters, input shaping and the like are used, the energy components corresponding to resonance frequency are cut by notch filters or input shaping, so that residual vibration is reduced. However, since these filters change the commanded path in compensation for reduction of the residual vibration, there occurs a phenomenon that the machine cannot be driven following the commanded path the user has programmed. For example, when the commands are processed through notch filters, generally overshoot occurs. It is easily understood there from that step response of notch filters causes overshoot. If use of notch filters causes an overshoot in the commanded path, traces corresponding to the overshoot are left on the workpiece, hence degrading machining quality.